实体未使用 EclipseLink 持久化
Entity is not persisted using EclipseLink
我正在学习 JPA。在下面的代码中,我试图坚持Point
,然后列出Points
进行检查,结果发现它没有被保存。为什么?
谢谢!
PersistenceProvider provider = new PersistenceProvider();
EntityManagerFactory emf = provider.createEntityManagerFactory("sample", null);
EntityManager em = emf.createEntityManager();
// DROP TABLE POINT
// CREATE TABLE POINT (ID BIGINT NOT NULL, X DOUBLE, Y DOUBLE, PRIMARY KEY (ID))
// DELETE FROM SEQUENCE WHERE SEQ_NAME = 'SEQ_GEN'
// SELECT * FROM SEQUENCE WHERE SEQ_NAME = 'SEQ_GEN'
// INSERT INTO SEQUENCE(SEQ_NAME, SEQ_COUNT) values ('SEQ_GEN', 0)
Point p = new Point(1, 1);
em.persist(p);
// UPDATE SEQUENCE SET SEQ_COUNT = SEQ_COUNT + ? WHERE SEQ_NAME = ?
// bind => [2 parameters bound]
// SELECT SEQ_COUNT FROM SEQUENCE WHERE SEQ_NAME = ?
// bind => [1 parameter bound]
em.close();
EntityManager em2 = emf.createEntityManager();
Query query = em2.createQuery("select p from Point p");
List list = query.getResultList();
// SELECT ID, X, Y FROM POINT
System.out.println("Found objects: " + list.size());
// Found objects: 0
for (Object elt: list){
System.out.println(elt);
}
因为你在那里没有事务,所以什么都没有提交。
一些 JPA 提供程序将允许 "non-transactional" 写入(您在那里尝试执行的操作,例如 DataNucleus JPA),但许多不允许,因此您需要执行
em.getTransaction().begin();
... (persist, merge, remove calls)
em.getTransaction().commit();
如果您想要独立于供应商的持久性代码
我正在学习 JPA。在下面的代码中,我试图坚持Point
,然后列出Points
进行检查,结果发现它没有被保存。为什么?
谢谢!
PersistenceProvider provider = new PersistenceProvider();
EntityManagerFactory emf = provider.createEntityManagerFactory("sample", null);
EntityManager em = emf.createEntityManager();
// DROP TABLE POINT
// CREATE TABLE POINT (ID BIGINT NOT NULL, X DOUBLE, Y DOUBLE, PRIMARY KEY (ID))
// DELETE FROM SEQUENCE WHERE SEQ_NAME = 'SEQ_GEN'
// SELECT * FROM SEQUENCE WHERE SEQ_NAME = 'SEQ_GEN'
// INSERT INTO SEQUENCE(SEQ_NAME, SEQ_COUNT) values ('SEQ_GEN', 0)
Point p = new Point(1, 1);
em.persist(p);
// UPDATE SEQUENCE SET SEQ_COUNT = SEQ_COUNT + ? WHERE SEQ_NAME = ?
// bind => [2 parameters bound]
// SELECT SEQ_COUNT FROM SEQUENCE WHERE SEQ_NAME = ?
// bind => [1 parameter bound]
em.close();
EntityManager em2 = emf.createEntityManager();
Query query = em2.createQuery("select p from Point p");
List list = query.getResultList();
// SELECT ID, X, Y FROM POINT
System.out.println("Found objects: " + list.size());
// Found objects: 0
for (Object elt: list){
System.out.println(elt);
}
因为你在那里没有事务,所以什么都没有提交。
一些 JPA 提供程序将允许 "non-transactional" 写入(您在那里尝试执行的操作,例如 DataNucleus JPA),但许多不允许,因此您需要执行
em.getTransaction().begin();
... (persist, merge, remove calls)
em.getTransaction().commit();
如果您想要独立于供应商的持久性代码